1. Field of the Invention
This invention is a system and related methods of manufacture and use that combine medical device implants with bioactive agent delivery. More specifically, it is an implantable stent system and related methods of use. Still more specifically, it is a system that includes an implantable stent in combination with gamma-tocopherol agent delivery.
2. Description of Related Art
Implantable stents have been under significant development for more than a decade, and many different designs have been investigated and made commercially available for use in providing mechanical scaffolding to hold body lumens, including in particular blood vessels, and more specifically coronary and peripheral arteries. Other body lumens where stents have been disclosed for use include pulmonary veins, gastro-intestinal tract, biliary duct, fallopian tubes, and vas deferens. Still further, artificial lumens have been created in the body in a man-made effort to provide artificial communication or transport within the body, such as for example shunts, and transmyocardial revascularization, and stents have been disclosed for intended use in these lumens as well.
Vascular stents are generally tubular members formed from a lattice of structural struts that are interconnected to form an integrated strut network that forms a wall that surrounds an axis. The integrated strut lattice typically includes inter-strut gaps through which the inner lumenal axis within the stent wall and outer region surrounding the stent wall are able to communicate. This is beneficial for example in the setting of stent implantation along a length of a main lumen, e.g. an artery, where side branches may beneficially receive flow from the main lumen through the gaps in the stent wall.
The majority of commercially available stents form completely integrated tubular structures, with continuity found along the integrated strut lattice both circumferentially as well as longitudinally. In order to provide for the adjustability between the collapsed and expanded conditions, such stents generally incorporate undulating shapes for the struts, which shapes are intended to reconfigure to allow for maximized radial expansion with minimized longitudinal change along the stent length. This is generally desirable for example in order to achieve repeatable, predictable placement of the stent along a desired length of localized, diseased region to be re-opened (e.g. occlusion), as well as maintain stent coverage over the expanding balloon at the balloon ends. Else, a stent that substantially shortens during balloon expansion exposes the balloon ends to localized vessel wall trauma at those ends without the benefit of the stent scaffolding to hold those regions open long-term after the intervention is completed.
Notwithstanding the prevalence of the foregoing type of stent just described, other designs have also been disclosed that either further modify such general structures, or further depart from the basic design. For example, one additional type of stent forms a wall that is not circumferentially continuous, but has two opposite ends along a sheet formed from the strut lattice. This sheet is adjusted to the collapsed condition by rolling the stent from one end to the other. At the site of implantation, the stent is unrolled to form the structural wall that radially engages the lumenal wall and substantially around an inner lumen. In the event the stent is undersized to the lumen, the opposite ends overlap and thus double the thickness of implant material that protrudes from the lumen wall and into the lumen. In another example, stents have been disclosed that form a helical structure along a vessel wall when implanted, which approach has been in particular promoted for beneficial treatments of peripheral vessels such as superficial femoral artery (SFA) implants due to resistance to kinking during stress of axial or longitudinal movement.
Stents are most frequently used in an interventional recanalization procedure, adjunctive to methods such as balloon angioplasty, or atherectomy such as rotational atherectomy devices and methods. “Balloon expandable” stents are generally constructed from a material, such as stainless steel or cobalt-chromium alloy for example, that is sufficiently ductile to be delivered in a collapsed condition on an outer surface of a deflated balloon, and is then expandable by inflation of the balloon to an expanded condition against the subject lumenal wall and that is substantially retained in such condition as an implant upon subsequent balloon deflation. “Self-expanding” stents are generally constructed of an elastic, super-elastic or shape-memory material, such as particular metal alloys including for example nickel-titanium alloys. These materials typically have a memory state that is expanded, but is delivered to the implantation site in a collapsed condition for appropriate delivery profiles. Once in place, the stent is released to recover or “self-expand” against the lumenal wall where it is then left as the implant.
Stents are typically intended to maintain patency, other uses have been disclosed. For example, some stents have been disclosed for the purpose of occluding the subject lumen where the stent is implanted. Examples of such stents include fibrin coated stents, and examples of such occlusive uses for stents include fallopian tubal ligation and aneurysm closure.
Stents have been further included in assemblies with other structures, such as grafts to form “stent-grafts”. These assemblies generally incorporate a stent structure that is secured to a graft material, such as formed from a textile or sheet material type construction. Examples of uses that have been disclosed for stent-grafts include for example aneurysm isolation, such as in particular along the abdominal aorta wall.
In the particular setting of vascular stenting, stents have had an enormous impact upon the occurrence of “restenosis” following recanalization procedures. “Restenosis” is a re-occlusion of the acutely recanalized blockage that typically takes place within 3-6 months after intervention, and is generally a combination of mechanical and physiological responses to the vessel wall injury caused by the recanalization procedure itself. In one regard, restenosis can occur at least in part from an elastic recoil of the expanded vessel wall, such as following expansion of the wall during balloon angioplasty. With respect to the physiological response to injury, it has generally been observed that injury from the recanalization to the intimal, medial, and sometimes adventitial layers of a vessel wall causes smooth muscle cells within the wall to undergo aggressive mitosis and hyperproliferation, dividing and migrating into the vessel lumen to form a “scar” that occludes the vessel lumen. Whereas angioplasty and other recanalization interventions prior to the advent of stenting resulted in approximately 30%-50% restenosis rate, stenting has generally reduced this rate to about 20%-30%, which reduction is considered at least in part a result of the mechanical prevention of vascular recoil.
Recent efforts in vascular stenting have been intended to incorporate additional therapy adjunctive to stenting to further reduce the incidence of restenosis. Some efforts for example have been intended to locally deliver therapeutic doses of radiation to the vessel wall concomitant to stenting, including for example by incorporating radioactive materials into or on the stent scaffolding itself. However, these efforts carry significant burden peri-operatively in handling and disposing of the materials, and results have yet to be considered compelling among substantial portions of the healthcare community. Moreover, local energy delivery such as via radioactive stents is substantially different than local elution delivery of materials and compounds from stents which are thereafter subject to diffusion, flow, and other active transport mechanisms.
More recently, a substantial industry effort has been underway to incorporate local drug delivery to stented lesions specifically to retard and prevent restenosis. A molecular approach is considered a highly beneficial solution for the restenosis problem (Sousa et al. Circ 2003; 107:2274-2279). For example, various local delivery devices have been disclosed to provide highly localized injection of anti-restenosis material into the injured wall, such as via micro-needles incorporated onto the outer skin of expandable balloons.
A more substantial effort, however, has been to incorporate the anti-restenosis drugs on or into the stents themselves in a manner such that the stent elutes the drug into the vessel wall over a prescribed period of time following implantation, otherwise known as drug eluting stents (“DES”). Examples of devices intended for this use include coated stents, which provide a stent structure with an outer coating that holds and elutes the drug.
The most prevalent form of coatings disclosed for use in DES devices include polymers, such as for example in one particular commercial embodiment a two-layer polymer coating with one layer holding drug and another layer retarding elution to provide drug release over an extended period of time, or with one layer providing adhesion to the underlying stent metal and the other layer holding and eluting the drug. Other examples of DES coatings include ceramics, hydrogels, biosynthetic materials, and metal-drug matrix coatings.
Examples of drugs that have been investigated for anti-restenosis uses such as via DES methods include anti-mitotics, anti-proliferatives, anti-inflammatory, and anti-migratory compounds. Further examples of compounds previously disclosed for use in DES devices and methods include: angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor antagonists, anti-sense materials, anti-thrombotics, platelet aggregation inhibitors, iron chelators (e.g. exochelin), everolimus, tacrolimus, vasodilators, nitric oxide, and nitric oxide pressors or promoters.
Two more specific compounds that have been under substantial clinical investigation on DES devices include sirolimus and paclitaxel. These DES efforts have made substantial strides toward reducing restenosis rates from the typical rate in stented lesions of about 20% to about 35%, to a reduced rate generally around, or in some populations possibly below, about 10%.
Notwithstanding the substantial improvements that appear to be anticipated in view of the recent sirolimus and paclitaxel DES clinical experiences, however, various concerns still remain and various needs also still remain that with respect to these and other previously disclosed DES efforts. For example, the reduced restenosis rates experienced may be driven lower with drugs with still more potent efficacy. Moreover, concerns remain regarding other possible harmful effects of the interventional drug approaches which block aspects of the smooth muscle cell cycle, e.g. toxicity, weakening of the vessel lining, late loss, negative remodeling, and possible aneurysm formation.
In one regard, certain drugs have been promoted for such use in preventing restenosis by virtue of their “pro-healing” bioactivity, often associated with promoting re-endothelialization of the injured region of lumen where the stent is implanted. More specifically, during stent placement in blood vessels, the vessel injury that typically initiates the cascade of events of the restenosis cycle includes denudation of the endothelium along the vessel lining. Endothelium lines the vessel wall and provides, among other things, a barrier between the smooth muscle cell lining of the vessel wall and various factors within blood pool of the inner lumen. Once denuded of the endothelium, and frequently also concomitant with breaking of an elastic lamina barrier between the endothelium and media/adventitia, these factors are exposed to the muscle cells and initiate the restenosis cascade to mitosis, migration, and hyper-proliferation into the vessel. Accordingly, promoting re-endothelialization, and hence re-establishing the barrier against the restenosis pressors from the blood pool, has been promoted as a viable, less traumatic, and highly advantageous approach to preventing restenosis. Moreover, by preventing the proliferation via healing from rapid re-endotheliazation, many side effects concomitant with various cytotoxic or other “anti-proliferative” agent approaches are avoided, including for example weakening of the wall, negative remodeling, and possible aneurysm formation, are avoided.
One example of a “pro-healing” approach intended to treat restenosis includes delivering VEGf as a growth factor to promote endothelialization of an injured vessel wall. Another example of a “pro-healing” approach intended to promote re-endothelialization over a stent provides anti-bodies on a stent surface which are intended to attract adhesion of endothelium. None of these approaches have yet been shown to provide sufficient safety and efficacy to prevent restenosis to be advanced to widespread commercial use. Other approaches to promote “re-endothelialization” of stented vessels would provide substantial benefit to patients and healthcare in general.
Pleiotrophin (PTN) is another growth factor that has been previously investigated for promoting angiogenesis and has also been observed as a potent agent to promote self-limiting tissue proliferation, and in particular regard to endothelium, believed useful for “wound healing” applications. Incorporation of this growth factor with stenting procedures and otherwise for vascular healing, e.g. endothelialization of vascular or other lumen linings to heal wall injury and prevent restenosis, is considered a substantial benefit.
Notwithstanding the wide variety of compounds that have or are being investigated for restenosis therapy/prevention, presently approved drugs for preventing restenosis are generally considered toxic compounds. Each presents substantial risk of certain undesirable effects aside from the benefit afforded by their local delivery. A substantial goal of restenosis prevention via stent delivery in particular is to prevent the restenotic response with as low a dose as possible, while preventing other harmful effects such as vessel remodeling, thrombosis, inflammation, allergic reaction, cellular apoptosis, etc. In this regard, more pro-healing approaches and related compounds have become the topic of substantial investigation, but have yet to be approved or used in mainstream medicine. In another regard, combined delivery of multiple compounds in “cocktail” formulation has also become an interesting topic of investigation. In particular, certain anti-inflammatory agents have been investigated for stent elution in combined form with other potent anti-proliferative or anti-mitotic compounds.
Vitamin E is a compound that has been variously disclosed in the past related to wound healing, and in particular protection against keloid scarring, a hyperproliferative response to injury that shares certain biochemical similarities with vascular restensosis. Vitamin E is remarkably safe, and falls within a class of compounds that are “generally regarded as safe” or “GRAS”. Vitamin E is available in several forms that present varied activities between them. Whereas alpha-tocopherol has been widely investigated for therapeutic uses, until recently gamma-tocopherol (a form of “des-methyl tocopherol”) has received much less attention in science. However, gamma-tocopherol presents a variety of beneficial advantages over alpha-tocopherol in various considerations. In one particular regard, gamma-tocopherol has been characterized to exhibit much more potent anti-oxidant qualities, resulting in a unique anti-inflammatory activity not shared with the alpha-tocopherol. In addition, gamma-tocopherol is believed to enhance outcomes of therapy when combined with certain other bioactive agents or drugs. Notwithstanding these beneficial characteristics, gamma-tocopherol has not heretofore been disclosed for use as a therapeutic agent for treating restenosis or otherwise for delivery via or with stents, either alone or in combination with other bioactive agents.
A need remains for local delivery of safe and efficacious anti-inflammatory and healing agents to treat abnormal lumenal wall conditions.
A need remains in particular for local delivery of such a compound so as to promote wound healing of blood vessels and other lumens in response to injury, such as associated with recanalization or stent implantation interventions.
Much benefit may be provided by delivering gamma-tocopherol, or a precursor, analog, or derivative thereof, or another compound sharing similar characteristics with gamma-tocopherol, to injured lumenal walls following endolumenal stent implantation or otherwise in order to provide local therapy to adverse lumenal wall conditions.